A percussion hammer such as described in French patent 2,596,681 is used with a pressure source having a high-pressure side and a low-pressure side and with a tool having a shaft with a rear end. This hammer has a housing formed with an axis-defining bore having a front end in which the tool shaft is normally coaxially engaged. A piston coaxially displaceable in the bore has a forwardly directed face defining in the bore a front return chamber of small effective piston surface area, and a rearwardly directed face defining in the bore a rear drive chamber of larger effective surface area. The front chamber is permanently connected with the high pressure side of a pressure source and a reversible control valve is connected between both sides of this source and the rear chamber for alternately pressurizing and depressurizing the rear chamber and thereby alternately displacing the piston axially forward to a front position in which it strikes the rear end of the tool shaft and axially backward away from the tool. At least one recoil-damping sleeve surrounds the piston axially ahead of the front chamber and has a front end operatively engageable axially forwardly with the tool shaft and a rear end defining with-the bore and with the piston front face a recoil chamber separated from the front return chamber when the piston is in or axially forward of its front position and communicating therewith when the piston is axially backward of its front position.
Thus with this system the recoil chamber is completely closed when the piston is in its front position when a recoil shock wave is generated, but opens into the front chamber once the piston moves back. The energy of the recoil shock wave is transmitted to the fluid in this chamber by the recoil sleeve or sleeves, thereby damping this force and eliminating noise and vibration. In addition a portion of the energy damped is transmitted to the piston at its front face so that it is actually used to start the piston on its return stroke. This energy is therefore used to do some necessary work and is not wasted.
Once the piston has recoiled a little the recoil chamber is opened up into the front return chamber so that it does not need its own fluid-feed passage. This simplifies the construction of the apparatus. Furthermore due to the location of this recoil chamber right next to the front return chamber it does not complicate the machine by making it necessary to build it larger.
The sleeve is constituted by a front sleeve having a front end in operative engagement with the tool shaft, an intermediate sleeve having inner and outer seals respective bearing on the piston and bore, and a rear sleeve having a rear end forwardly axially delimiting the recoil chamber. The front sleeve has cylindrical front and rear portions joined by a frustoconical intermediate portion. The tool shaft has an enlarged region and the recoil sleeve directly engages same. In addition or alternately the device comprises a drive element rotatable in the housing about the axis and rotationally but not axially coupled to the tool shaft and the sleeve directly engages this drive element.
Such an arrangement has the disadvantage that the rotary parts turning the bit are frequently subjected to considerable hammering. When there is no tool in the device or the tool is out of contact with the workpiece, the sleeve can push forward against the rotating drill, causing considerable wear.